This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
3GPP third generation partnership project
UTRAN universal terrestrial radio access network
EUTRAN evolved UTRAN (LTE)
LTE long term evolution
Node B base station
eNB EUTRAN Node B (evolved Node B)
UE user equipment
UL uplink (UE towards eNB)
DL downlink (eNB towards UE)
EPC evolved packet core
MME mobility management entity
S-GW serving gateway
MM mobility management
HO handover
PDU protocol data unit
PHY physical
RLC radio link control
RRC radio resource control
RRM radio resource management
MAC medium access control
PDCP packet data convergence protocol
O&M operations and maintenance
CQI channel quality indicator
SC-FDMA single carrier, frequency division multiple access
PUCCH physical uplink control channel
SRS sounding reference signal
DRX discontinuous reception
TAT time alignment timer
TA time alignment/timing advance
SCH shared channel
RACH random access channel
LCD logical channel identifier
The specification of a communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) has been addressed within 3GPP. In this system the DL access technique will be OFDMA and the UL access technique will be SC-FDMA.
One specification of interest to these and other issues related to the invention is 3GPP TS 36.300, V8.4.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8).
FIG. 1 reproduces FIG. 4 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1-MME interface and to a Serving Gateway (S-GW) by means of a S1-U interface. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:
functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
selection of a MME at UE attachment;
routing of User Plane data towards Serving Gateway;
scheduling and transmission of paging messages (originated from the MME);
scheduling and transmission of broadcast information (originated from the MME or O&M); and measurement and measurement reporting configuration for mobility and scheduling.
The E-UTRAN RRC-CONNECTED mode defines both DRX and periodic transmission of the CQI report. Additionally, it is understood that the periodic reporting of CQI and the transmission of SRS is masked with the DRX pattern such that the periodic CQI report and SRS are only sent during DRX on-duration, or alternatively during an active time. In addition, the transmission of periodic CQI and SRS are only performed so long as the UE has PUCCH resources allocated.
If the UE is in a cell in which PUCCH resources are not invalidated due to, for example, an uplink timing alignment timeout, a situation may arise that results in excessive UE power consumption, or less than optimum efficiency.
Another specification of interest is 3GPP TS 36.321 V8.2.0 (2008-05), Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification (Release 8).
In the E-UTRAN stage 3 MAC specifications reflected in 3GPP TS 36.321 it is stated in section 5.2 that the UE has a configurable time alignment timer (TAT). The TAT is valid only in the cell for which it was configured and started. It is further stated that when the TAT expires the UE is to release all PUCCH resources and release any assigned SRS resources.
A parameter range that has been under discussion related to the validity time for the TAT is between 500 ms and infinite (i.e., the TAT never expires).
Additionally, the UE can be configured to send periodic CQI reports and SRS in the UL. According to 3GPP TS 36.300 both of these parameters will be sent according to Stage 2 DRX rules. That is, when DRX is configured the periodic CQI reports can only be sent by the UE during the “active-time”. RRC can further restrict periodic CQI reports so that they are only sent during the on-duration. This means that if the UE is configured with periodic CQI and/or SRS the UE shall transmit these in the UL as long as the TAT is valid.
For small cells (macro or home cells) it may not be necessary to change the TA within the cell. This implies that the value of the TA is static and does not vary due to UE movement within the cell and, as a result, the TAT can be set to infinite.